Self-locking fan shaft bearing

ABSTRACT

A self-locking threaded bushing is provided for mounting a steel fan shaft in an aluminum support. The bushing is threaded so that it may be threaded into the aluminum structure. The bushing is provided with a bore corresponding to the shaft diameter such that a normal press fit is established when the shaft is initially pressed into the bushing. A reduced diameter portion of the bushing bore results in an interference fit between the shaft and the bore. Relief cuts in the bushing allow the bushing to expand in the vicinity of the reduced diameter portion as a result of interference from the shaft. The expansion of the bushing results in an interference fit between the threads of the bushing and those of the aluminum structure such that the bushing and shaft are essentially locked in place until such time as the shaft is extracted from the bushing.

FIELD OF THE INVENTION

[0001] The present invention relates generally to cooling fans for internal combustion engines. More particularly, the present invention relates to means for mounting a fan bearing/shaft to the engine. Specifically, the present invention relates to a bushing for press fitting a fan bearing/shaft into the timing gear cover.

BACKGROUND OF THE INVENTION

[0002] Cooling fans for internal combustion engines are commonly journaled on a fan shaft by way of bearing which is press fit to the shaft and to the fan hub. The fan shaft is often mounted to the timing gear cover at the front of the engine. Common means for attaching the fan shaft to the timing gear cover have included press fitting the shaft directly in a bore provided in the timing gear cover or by threading a bushing into a threaded bore in the timing gear cover and press fitting the fan shaft into the bushing. Both methods have significant drawbacks. More particularly, timing gear covers are typically made from aluminum or aluminum alloy while the fan shaft is typically made from steel, thus press fitting steel directly into aluminum results in an inadequate press fit due yielding of the aluminum material and the differences in the coefficients of expansion between steel and aluminum. By using a threaded bushing the problems of the steel-aluminum press fit are avoided, but vibration and cyclical loading commonly cause the bushing to back-out of the threaded bore. Attempts at using chemical thread locking agents have proven unsuccessful in alleviating this problem. Accordingly, there is a clear need in the art for a means to mount a fan shaft to a timing gear cover of an internal combustion engine that will avoid problems of a steel-aluminum press fit without creating the additional drawbacks of known threaded bushings.

SUMMARY OF THE INVENTION

[0003] In view of the foregoing, it is an object of the invention to provide an improved means for mounting a steel fan shaft into an aluminum timing gear cover.

[0004] Another object of the invention is the provision of an improved means for mounting a steel fan shaft into an aluminum timing gear cover which positively maintains the shaft in the cover despite vibration and cyclical loading without the need for additional locking means.

[0005] A further object of the invention is to provide an improved means for mounting a steel fan shaft into an aluminum timing gear cover without the problems associated with pressing a steel shaft or bushing into an aluminum cover.

[0006] The foregoing and other objects of the invention together with the advantages thereof over the known art which will become apparent from the detailed specification which follows are attained by a self-locking bushing for mounting a fan shaft in a support structure having a threaded bore comprising: a cylindrical main body portion having a threaded outer diameter wherein the bushing is threaded into the threaded bore of the support structure; a first concentric bore in the main body portion for receiving the fan shaft, the first concentric bore having a diameter corresponding to an outer diameter of the fan shaft such that a normal press fit is established between the bushing and the fan shaft; a second reduced diameter bore in the main body portion wherein an interference fit is established between the bushing and the fan shaft; a plurality of relief cuts in the main body portion proximal to the reduced diameter bore wherein the main body portion of the bushing is allowed to expand in response to the interference fit between the bushing and the fan shaft so that an interference fit is established between the threaded outer diameter of the main body portion and the threaded bore of the support structure.

[0007] In general, a self-locking threaded bushing is provided for mounting a steel fan shaft in an aluminum support. The bushing is threaded so that it may be threaded into the aluminum structure. The bushing is provided with a bore corresponding to the shaft diameter such that a normal press fit is established when the shaft is initially pressed into the bushing. A reduced diameter portion of the bushing bore results in an interference fit between the shaft and the bore. Relief cuts in the bushing allow the bushing to expand in the vicinity of the reduced diameter portion as a result of interference from the shaft. The expansion of the bushing results in an interference fit between the threads of the bushing and those of the aluminum structure such that the bushing and shaft are essentially locked in place until such time as the shaft is extracted from the bushing.

[0008] To acquaint persons skilled in the art most closely related to the present invention, one preferred embodiment of the invention that illustrates the best mode now contemplated for putting the invention into practice is described herein by and with reference to, the annexed drawings that form a part of the specification. The exemplary embodiment is described in detail without attempting to show all of the various forms and modifications in which the invention might be embodied. As such, the embodiment shown and described herein is illustrative, and as will become apparent to those skilled in the art, can be modified in numerous ways within the spirit and scope of the invention—the invention being measured by the appended claims and not by the details of the specification.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] For a complete understanding of the objects, techniques, and structure of the invention reference should be made to the following detailed description and accompanying drawings, wherein:

[0010]FIG. 1 is an exploded perspective view of a fan assembly using the bushing according to the invention;

[0011]FIG. 2 is a perspective view of the bushing according to the invention; and,

[0012]FIG. 3 is a cross-sectional view of the bushing taken along the line 3-3 of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0013] With reference to FIG. 1 it will be seen that a cooling fan assembly is designated generally by the numeral 10. Assembly 10 includes a timing gear cover 12, a bushing 14, a fan shaft 16, a fan bearing 18 and a fan hub 20. Fan shaft 16 and fan bearing 18 may be a unitary assembly wherein the fan shaft acts as the inner race of the bearing or a separate bearing may be pressed onto the shaft. In either case the fan hub 20 includes a bore 22 into which the bearing 18 is press fit allowing the fan hub to turn freely with respect to shaft 16. Fan blades (not shown) are appropriately affixed to the fan hub 20.

[0014] Referring now to FIGS. 2 and 3 it will be seen that bushing 14 has a generally cylindrical main body portion 23 member having a concentric bore 24 extending the entire length of thereof. Bushing 14 also includes threads 26 on its outer diameter and may include a flanged portion 28 at a first end 30. For reasons which will become apparent as the description continues, bore 24 of bushing 14 includes a reduced diameter portion 32 proximal to a second end 34. A plurality of relief cuts 36 are provided in bushing 14 proximal the reduced diameter portion 32.

[0015] A bore 38 is provided in timing gear cover 12 for receiving bushing 14. Accordingly, bore 38 includes threads 40 so that bushing 14 may be threaded therein. During assembly the bushing 14 is first threaded into the timing gear cover 12 and then the fan shaft 16 is pressed into the bore 24 of bushing 14. The diameters of the bore 24 and the fan shaft 16 correspond such that a normal press fit is established between the shaft 16 and the bushing 14 when the shaft 16 is initially fitted in the bushing 14. When the shaft 16 is pressed into the bore 24 to the extent that the end of the shaft 16 reaches the reduced diameter portion 32 a normal press fit is no longer possible. This interference fit, in conjunction with the relief cuts 36 in bushing 14, cause the second end 34 of bushing 14 to flare outward somewhat to accommodate the shaft diameter. This results in an interference fit between the threads 26 of the bushing 14 and the threads 40 of the bore 38. As such the bushing 14 is locked in place and cannot be readily removed until such time as the shaft 16 is extracted from the bore 24.

[0016] It should now be apparent that the bushing of the present invention provides an improved means for mounting a steel fan shaft in an aluminum timing gear cover. Because of the interference fit between the threads of the bushing and those of the cover, the bushing and thus the fan shaft are positively maintained in place despite vibration and cyclical loading, without the need for additional locking means. Further, due to the threaded mounting arrangement, the problems associated with press fitting a steel shaft or bushing into an aluminum cover are obviated.

[0017] Thus it can be seen that the objects of the invention have been satisfied by the structure presented above. While in accordance with the patent statutes, only the best mode and preferred embodiment of the invention has been presented and described in detail, it is not intended to be exhaustive or to limit the invention to the precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiment was chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly and legally entitled. 

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
 1. A self-locking bushing for mounting a fan shaft in a support structure having a threaded bore comprising: a cylindrical main body portion having a threaded outer diameter wherein the bushing is threaded into the threaded bore of the support structure; a first concentric bore in the main body portion for receiving the fan shaft, the first concentric bore having a diameter corresponding to an outer diameter of the fan shaft such that a normal press fit is established between the bushing and the fan shaft; a second reduced diameter bore in the main body portion wherein an interference fit is established between the bushing and the fan shaft; a plurality of relief cuts in the main body portion proximal to the reduced diameter bore wherein the main body portion of the bushing is allowed to expand in response to the interference fit between the bushing and the fan shaft so that an interference fit is established between the threaded outer diameter of the main body portion and the threaded bore of the support structure.
 2. A self-locking bushing for mounting a fan shaft in a support structure having a threaded bore as set forth in claim 1 wherein the main body portion has four relief cuts equally spaced about the diameter thereof.
 3. A self-locking bushing for mounting a fan shaft in a support structure having a threaded bore as set forth in claim 3 wherein the bushing further includes a flanged portion at a first end thereof. 